1. Field of the Invention
The invention relates to a developing apparatus for use in a copying machine, a laser beam printer, a facsimile apparatus a printing apparatus or the like using an electrophotographic process or an electrostatic recording process.
2. Description of Related Art
Heretofore, in visualizing an electrostatic latent image formed on an image bearing member, there has been widely used a two-component developing method using a two-component developer comprising a nonmagnetic toner and a magnetic carrier. In this two-component developing method, the developer agitated by agitating means in a developing apparatus is carried on a developer carrying member having therein a magnet which is magnetic field generating means, and the electrostatic latent image is visualized in a portion opposed to the image bearing member by the use of this developer.
In a two-component developing apparatus adopting such a two-component developing method, only the toner is supplied for use from a toner supplying container discretely provided and therefore, the toner density (i.e., the rate of the toner particle weight to the total weight of carrier particles and toner particles) of the two-component developer is a very important factor in stabilizing the quality of an image.
Now, the toner particles in the developer are consumed during development and therefore the toner density changes at all times. Thus, it is necessary to accurately detect the toner density of the developer at a suitable time by the use of a developer density controller (ATR), effect toner supply in conformity with changes in the toner density, effect agitation sufficiently and control the toner density always at a constant level to thereby maintain the excellence of an image.
In order to correct the changes in the toner density in the developing apparatus by developing, as described above, that is, in order to control the amount of toner supplied to the developing apparatus, as a toner density detector and a density controller for the developer in a developing container, a number of various types have heretofore been put into practical use.
Use is made, for example, of a developer density controller installed at a location proximate to a developing sleeve or the developer carrying route of the developing container, for detecting and controlling the toner density by the utilization of the fact that the developer carried onto the developing sleeve or the developer in the developing container differs in the reflectance when light is applied thereto depending on the toner density, or a developer density controller of an inductance detection type designed to detect the density of the toner in the developing container by a detection signal from an inductance head for detecting the apparent permeability by the mixing ratio between the magnetic carrier and the nonmagnetic toner on the side wall of the developer and converting it into an electrical signal, and supply the toner by the comparison thereof with a reference value.
Also, there is a method whereby the density of a patch image formed on a photosensitive drum as an image bearing member is read by a light source provided at a location opposed to the surface of the photosensitive drum and a sensor for receiving the reflected light thereof, and the read image density is converted into a digital signal by an analog-to-digital converter and thereafter is sent to a CPU, and if in the CPU, the density is higher than an initial set value, toner supply is stopped until the density restores the initial set value, and if the density is lower than the initial set value, the toner is forcibly supplied until the density is restored to the initial set value, and as a result, the toner density is indirectly maintained at a desired value.
A popular two-component developing apparatus will be described here with reference to FIG. 14A of the accompanying drawings.
In FIG. 14A, the developing apparatus 400 is comprised of a developing container 10 containing a developer therein, a developing sleeve 1 which is a developer carrying member which is a rotary hollow cylinder, a magnet roller 2 which is magnetic field generating means fixedly disposed in the developing sleeve 1 relative to the rotation thereof, carrying screws 4a and 5a which are developer agitating and carrying means disposed in the developing container 10, and a regulating blade 3 which is a developer layer thickness regulating member disposed to form a thin layer of developer on the surface of the developing sleeve 1.
A design is made such that a DC bias and an AC bias are applied from a voltage source (not shown) to the developing sleeve 1. Generally, when the AC bias is applied, developing efficiency increases and an image assumes high excellence.
Here, a description will be made of a developing step of visualizing an electrostatic latent image formed on a photosensitive drum 103 which is an image bearing member by a two-component magnetic brush method by the use of the developing apparatus 400 shown in FIGS. 14A and 14B of the accompanying drawings, and a developer circulating system.
First, the developer scooped up onto the developing sleeve 1 by a magnetic pole N1 with the rotation of the developing sleeve 1 has its amount borne on the developing sleeve 1 regulated by the regulating blade 3 in the process of being carried from the magnetic pole N1 to a magnetic pole S1, and is formed as a thin layer on the developing sleeve 1. Here, when the developer formed as the thin layer is carried to the magnetic pole S1 which is a main developing pole, ears are formed by a magnetic force. The above-mentioned electrostatic latent image is developed by the developer formed into the shape of the ears, whereafter the developer on the developing sleeve 1 is returned into the developing container 10 by a repulsive magnetic field by the magnetic pole N1 and a magnetic pole N2 installed on the inner side of the magnet roller 2 which is adjacent to the interior of the developing container 10.
As described above, in the developing apparatus adopting the two-component developing method, magnetic poles of the same polarity are disposed side by side in the magnet 2 in the developing sleeve 1 adjacent to the interior of the developing container 10, whereby the developer after developing is once stripped off from the developing sleeve 1 so as not to leave the previous image hysteresis.
In a developing apparatus using as a developer a two-component developer having a carrier and a toner, it is desirable that the toner and the carrier be agitated well and carried. Again here, there is adopted a two-shaft agitating type in which the interior of the developing container 10 is divided into a developing chamber 4 located on the toner supply side to the photosensitive drum 103 and an agitating chamber 5 side for receiving the supply of the supplied toner, and screw-shaped agitating means 4a and 5a are disposed parallel with each other in the respective space portions. In the developing apparatus of the two-shaft agitating type, provision is made of the developing sleeve 1, a toner density sensor 6 and a toner container 50 for supply, and a circulation route for agitating and carrying the developer is constituted by the first agitating means 4a disposed in the developing chamber 4, and the second agitating means 5a disposed in the agitating chamber 5, and the carried developer is fed into and circulated in the respective chambers 4 and 5 from delivery portions formed on the end portion sides of the respective agitating means 4a and 5a. 
FIG. 14B shows the circulation route as it is seen from above. It has the developing sleeve 1 and the screws 4a and 5a which are the agitating means, and maintains an agitating property and a carrying property.
However, the downsizing of a developing apparatus itself has been required for the downsizing of recent monochromatic/color printers and monochromatic/color copies, and there is the task that a basic function is maintained by a small developing apparatus.
Regarding the downsizing, as a task when the developing apparatus itself is made small, a toner receiving port (supplying port) 8 for receiving (supplying) the toner from a toner supplying container 50 could heretofore be disposed outside the length of the developing sleeve 1 with respect to the lengthwise direction, but it is necessary to dispose the toner receiving port (supplying port) 8 within the length of the developing sleeve 1 in the lengthwise direction thereof. That is, when the developer is carried as shown in FIG. 14B, the toner supplying port 8 could be installed upstream of an area overlapping the developing sleeve 1 in the lengthwise direction thereof with respect to a developer carrying direction, and a distance sufficient for the supplied toner to arrive at the developing sleeve 1 could be kept.
In contrast, when the developing apparatus is downsized, the toner supplying port 8 is installed in an area overlapping the developing sleeve 1 in the lengthwise direction thereof as shown in FIG. 3B of the accompanying drawings, and the supplied toner is not sufficiently agitated, but there cannot be kept a distance at which the developer can be sufficiently agitated before delivered from the second agitating means 5a far from the developing sleeve 1 to the first agitating means 4a proximate to the developing sleeve 1 and therefore, the chargeability of the supplied toner was bad, and toner spatter, a fogged image and an uneven image occurred.
Herein, screw members are used as the first agitating means and the second agitating means provided in the developing apparatus of the construction as described above, and the first agitating means near to the developing sleeve which is a developer carrying member may be referred to as a first screw, and otherwise referred to herein as screw 5a, and the second agitating means far from the developing sleeve may be referred to as a second screw, and otherwise referred to herein as screw 5b, wherein the first and second screws are collectively referred to herein as the screws.
The occurrence phenomenon of a faulty image due to the faulty charging of the toner attributable to faulty agitation appeared remarkably after endurance. Also, with the downsizing of the developing apparatus, the carrying screws themselves also became smaller and the agitability and carrying property of the toner were further lowered to thereby make the above-noted problem difficult solve.